Oil base drilling fluid filtrate-effected sand consolidation

ABSTRACT

A permeable water-containing earth formation is consolidated while a borehole is being drilled into that formation by circulating as a drilling fluid an oil solvent solution containing a mixture of an epoxide and imine that forms an epoxy resin when mixed with water and a suspension of finely divided solid particles that forms a filter-cake permitting a selected amount of filtrate invasion into a permeable earth formation.

United States Patent 1 Suman, Jr. et al.

[ Aug. 7, 1973 01L BASE DRILLING FLUID FILTRATILEFFECTED SANDCONSOLIDATION Inventors: George 0. Suman, Jr., Edwin A.

Richardson, both of Houston; Ronald F. Scheuerman, Bellaire. all of Tex.

Assignee: Shell Oil Company, Houston, Tex.

Filed: Jan. 27, 1972 Appl. No.: 221,402

US. Cl. 175/72, 166/295, 252/85 M Int. Cl E211! 21/04, E2lb 33/138 Field01 Search 175/72, 65; 166/295;

References Cited UNITED STATES PATENTS 11/1940 Dawson et a1 252/85 M2,350,154 5/1944 Dawson ct a1 252/85 M 2,356,302 8/1944 Chapman 252/85 M3,294,166 12/1966 Havenaar et a1 166/295 3,294,168 12/1966 Bezemer et166/295 3,308,884 3/1967 Robichaux 166/295 3,339,633 9/1967 Richardson166/295 3,428,122 2/1969 Methven et 166/295 Primary Examiner-Stephen J.Novosad Attorney-Harold L. Denkler and H. W. Coryell [57] ABSTRACT 4Claims, No Drawings OIL BASE DRILLING FLUID FILTRATE-EFFECTED SANDCONSOLIDATION BACKGROUND OF THE INVENTION The invention relates to aprocess for drilling a borehole with an oil-based mud whileconsolidating a permeable water-containing earth formation into whichthe borehole is being drilled. The invention is particularly useful indrilling operations that are apt to encounter water-containingunconsolidated reservoir formations (which may also contain oil). Insuch situations, the invention improves the borehole stability, providesa consolidated reservoir formation to which cement can be more firmlybonded than it could to an unconsolidated earth formation and/orconsolidates to a selected depth a virgin reservoir formation which hasnot been previously invaded by any fluids other than the naturalreservoir fluids.

SUMMARY OF THE INVENTION The invention relates to drilling a boreholeinto a permeable water-containing earth fonnation while consol idatingparticles within the earth formation to form a permeable integralstructure. The borehole is drilled by circulating a drilling fluidcomprising an oil solvent solution of a mixture of epoxide and iminethat forms an epoxy resin when mixed with water and a suspension offinely divided solid particles that form a filter cake when screened outagains a permeable earth formation. The circulating drilling fluid ispressurized within the borehole to cause filtrate invasion of the earthformation and is maintained (i.e. is treated between recycles into theborehole) to provide a filtrate solution of resin forming componentsthat precipitates a partially cured epoxy resin when those componentsreact with the water within the earth formation.

DESCRIPTION OF THE INVENTION The present invention is at least in partpremised on a discovery that the drilling fluid filtrate invasion causedby the above drilling procedure adjusts the fluid content of a permeablewater-containing earth formation to that required for forming and curinga sand consolidating resin. The water concentration of such an earthform ation may range from substantially all water to only a residual orirreducible water saturation in a predominently oil-filled reservoir.When an oil-phase liquid, such as the presently described filtrate,flows through a peremable water-containing earth formation or reservoir,it tends to dissolve and miscibly displace substantially all oil-phasereservoir liquids that may be present while displacing some, andbypassing some, of

the aqueous liquids. As known to those skilled in the art, such asoil-phase liquid displacement tends to reduce the water concentration ofsuch a reservoir to a water-residual saturation. At such a residualsaturation, the water is usually present in amounts in the order of fromto 25 percent of the pore volume. Where the viscosity (at reservoirtemperature) of the oil-phase liquid that displaces reservoir fluids issubstantially l centipoise. the displacement leaves a substantiallyirreducible proportion of water that tends to be adsorbed on thereservoir rocks as a wetting phase which is distributed all along thewalls of the pores.

Those of the pores in a permeable water-containing reservoir which arelocated near enough to the borehole of a well being drilled inaccordance with the present invention to be penetrated by a plurality ofpore volumes of the drilling fluid filtrate, tend to be swept free ofany natural oil they may have contained. Such pores are left filled withonly the epoxide and iminecontaining filtrate and residual water. Insuch pores the water reacts with the imine and hydrolyzes it to theamine and the amine combines with the epoxide to form an epoxy resin.The present invention utilizes a discovery that the readily attainablerelative proportions of such reactants and reservoir fluids are suchthat it is feasible to conduct such a consolidation while drilling aborehole. When (I) the drilling fluid filtrate comprises a mixture ofaliphatic and aromatic hydrocarbons containing a resin-precipitatingproportion (such as about 18 percent by weight of the solution) of amixture of the epoxide and imine in substantially stoichemetricproportions (i.e., about 10 parts by weight of imine per parts by weightof epoxide) relative to resin-formation, and (2) enough filtrate flowsthrough an earth formation pore to reduce the water content of the porespace to an amount in the order of 25 percent of the pore volume, theproportions of water and imine are about stoichemetric with respect tothe hydrolysis of the imine. When the filtrate composition is soadjusted, the epoxy resin is formed, precipitates, becomes adsorbed onthe reservoir rock surfaces, and cures on those surfaces in a mannerthat consolidates any granular mass within the reservoir into apermeable integral structure. Those of the pore spaces within thereservoir which are located further away from the borehole arepenetrated by less of the drilling fluid filtrate and, ac cordingly, theextent of the sand consolidation decreases with distance away from thewell.

Oil solvent solutions of epoxy resin-forming components comprisingsolutions which are suitable for use as the drilling fluid filtrates ofthe present invention can contain a relatively wide variety ofcomponents and relative proportions. In general, such solutions arepreferably formulated in accordance with the teachings of the l-Iavenaarand Meys US. Pat. 3,294J66 which describes an epoxy resin precipitatingwell treating process for consolidating sand. In the present process thecuring agent is an amine in which the amino hydrogen atoms are covered(by reacting them with a ketone or aldehyde to form the imine). Theresin-forming solution components and proportions described in the abovepatent (such as: an oil solvent comprising mixed liquid hydrocarbonscontaining at least 50 percent by volume aromatic hydrocarbons; apolyepoxide; a polyfunctional amine, in imine-form, curing agent; apolymerization accelerator; reactant proportions that providepolymerization at a selected rate at the earth formation temperature;bonding agents; and the like) are particularly suitable for use in thepresent invention, and are incorporated herein by reference.

The imine which is used as a latent curing agent in the present drillingfluid filtrate can be a ketimine or aldimine of substantially any aminewhich is suitable for use as a curing agent in an epoxy resinformulation. The ketimines are preferred. Illustrative examples ofketimines which can be prepared by a direct reaction of a ketone with anamine (by procedures known to those skilled in the art) are listed inTable 1.

TABLE I Boiling Point of Ketirnine Itetone' Amine 'C mm Hg DMK EDA 44-41.0

(b) EDA Ethylene diamine DTA Diethylenetriarnine PDA Propylene diamineHMDA Hexamethylene diamine MXDA Methaxylylene diamine TEPA Tetraethylenepentamine (a) DMK Acetone MEK Methyl ethyl ketone MIBK Methyl isobutylketone DlBK Diisobutyl ketone MPK Acetophenone The finely divided solidparticles which are suspended in the present drilling fluid filtrates toform a filter cake can comprise substantially any filter cakeformingsolid particles which are substantially completely immiscible and inertwith respect to the oil solvent solution utilized as the filtrate. Suchfinely divided solids can comprise preyielded or prehydrated clays, suchas a prehydrated bentonite, Fuller's earth, aluminum silicates, calciumcarbonates, blown asphalts or the like, such as the materials describedin patents such as U.S. Pat. Nos. 2,223,027 or 2,350,154.

The sand consolidating drilling fluid of the present invention can alsocontain substantially any of various additives for improving thedrilling fluid properties as long as such additives are compatible withthe components and reactivity of the sand consolidating filtrate and thecontrolled filter loss properties of the drilling fluid. Such additivescan comprise: weighting materials, such as barites, iron or lead oxides,galena or the like; viscosity increasing agents or thickeners, such asthe partially hydrolyzed polyacrylamides or the like; corrosioninhibitors; etc.

The drilling fluid maintenance that is employed while drilling inaccordance with the present process should include the adjusting of thedrilling fluid filtrate composition to the extent required to provide afiltrate solution of resin forming components which precipitates apartially cured epoxy resin it reacts with the water in a permeablewater-containing earth formation. As known to those skilled in the art,the maintenance of an oil base drilling fluid should include adjustmentsof the fluid loss and/or viscosity imparting components as required tomaintain the selected fluid loss and reological properties. Water thatbecomes entrained in the circulating drilling fluid is preferablyremoved by surface treatments such as settling, centrifuging, or thelike. Particles of solidified epoxy resin which form within thecirculating drilling fluid are preferably removed by screening and/ordesanding or the like treatments. The concentration of the resin formingsolvents and/or reactants are preferably adjusted as required to providethe resin precipitating capability of the filtrate.

As known to those skilled in the art, finely divided suspended solidmaterials such as filter cake-forming solids and/or bit cutting solidstend to form relatively low permeability filter cakes on the permeableportions of the wall of a borehole. This occurs when the circulatingdrilling fluid is pressurized (by means of its hydrostatic head and/orsurface applied pump pressure) so that the liquid flows into the poresof a permeable earth formation while screening out the solids on thewall of the borehole. The filter cakes tend to become thickest and leastpermeable along the most permeable earth formations encountered by theborehole, since more fluid flows into them and causes more solids to bescreened out against them. The thickening of the filter cake decreasesthe rate of filtrate invasion into the adjacent earth formation and,thus, the filter cake tends to normalize the extent of the filtrateinvasion so that all portions of the formation are treated, since themore permeable portions do not receive proportionately larger amounts offiltrate.

The present process is particularly useful in drilling into an oil andwater containing reservoir formation that is or is apt to becomeunconsolidated. In a preferred procedure, the borehole is drilledthrough the overlying earth formations and into a zone near such areservoir formation by circulating one or more conventional types ofaqueous and/or oil base drilling fluids. A sand consolidating oil-basemud of the present type is preferably formulated at or near the welllocation and the composition of the drilling fluid being circulated isadjusted when desired to provide a circulation of the sand consolidatingoil-base drilling fluid of the present invention. The filtrate-eflectedsand consolidation provided by drilling through a permeablewatercontaining earth formation with the present drilling fluid canconvert an unconsolidated interval, such as those comonly encounterednear the Gulf of Mexico, from an interval which requires specialcompletion or treatment procedures (such as gravel packs, subsequentwell treatments to effect an in situ sand consolidation, or the like) toan interval that is comparable, in case of well completion andmaintenance, to a competent or well-cemented type of reservoir interval.

The present filtrate-effected sand consolidating drilling process isalso useful where it is desirable to effect a sand consolidationthroughout a relatively large portion of a permeable water-containingearth formation as soon as a borehole has been extended into at leastthe uppermost portion of that formation. For example, in numerousreservoirs near the Gulf of Mexico, the oilbearing sands are apt to beunconsolidated relatively thin stringers sandwiched betweensubstantially impermeable relatively thick layers or sections of shale.[n such stringers of unconsolidated sands, the vertical as well as thehorizontal permeabilities tend to be high. In addition, since the sandsare unconsolidated, substantially any backflow or production of fluidfrom the to the borehole is apt to remove significant portions of sandand form cavities around the well. In accordance with the presentinvention, when the top of such a layer has been encountered, theborehole advancing is preferably interrupted (for example, by takingweight off the bit and simply rotating and/or reciprocating the drillstring assembly) while circulating the drilling fluid. Such a procedureby itself tends to remove the filter cake or to increase itspermeability near the bottom of the borehole. This increases the amountof filtrate invasion so that, where the filtrate is the present sandconsolidating solution, it increases the depth of penetration below andaround the borehole of the sand consolidating treatment. Where desirablethe sand consolidating solution or drilling fluid filtrate can beinjected by setting a downhole packer or increasing the annulus pressureand injecting a relatively large slug of the sand consolidating solutioninto the reservoir in order to ef- 6 feet a consolidation for arelatively long distance becontaining earth formation. yond the bottomas well as around the borehole. 2. A process of claim 1 in which thesolvent compo- What is claimed is: nents of said oil solvent solutioncomprise a mixture of l. A sand consolidating drilling processcomprising: aliphatic and aromatic hydrocarbons that predomidrilling aborehole into a permeable water-containing 5 nates in aromatichydrocarbons.

earth formation while circulating an oil-base dril- 3. The process ofclaim 1 in which said oil-base drilling fluid comprising an oil solventsolution that ling fluid is formulated near a drilling site and thecomcontains a dissolved mixture of epoxide and imine position ofadrilling fluid being circulated while drilling that forms an epoxy resinwhen mixed with water a borehole is altered to provide said circulationof an and suspended finely divided solid particles that m oil-basedrilling fluid. form a filter cake when screened out against a per- 4.The process of claim 1 in which: meable earth formation; said drillinginto a permeable water-containing earth pressurizing the circulatingdrilling fluid within the formation is interrupted while the boreholereaches borehole to cause a filtrate invasion into a permean upperportion of an unconsolidated waterable water-containing earth formation;and 5 containing earth formation; and maintaining the chemicalcomposition of the circua slug of said oil-base drilling fluid having avolume lating drilling fluid so that its filtrate comprises a sufficientto permeate a selected relatively extensolution of resin-formingcomponents that precipisive portion of said unconsolidated earthformation tates a partially cured epoxy resin when the filtrate isinjected into the earth formation.

is mixed with the water in a permeable water-

2. A process of claim 1 in which the solvent components of said oilsolvent solution comprise a mixture of aliphatic and aromatichydrocarbons that predominates in aromatic hydrocarbons.
 3. The processof claim 1 in which said oil-base drilling fluid is formulated near adrilling site and the composition of a drilling fluid being circulatedwhile drilling a borehole is altered to provide said circulation of anoil-base drilling fluid.
 4. The process of claim 1 in which: saiddrilling into a permeable water-containing earth formation isinterrupted while the borehole reaches an upper portion of anunconsolidated water-containing earth formation; and a slug of saidoil-base drilling fluid having a volume sufficient to permeate aselected relatively extensive portion of said unconsolidated earthformation is injected into the earth formation.